The costliest metric in the investment decision

In almost every company, the same number decides which efficiency measures get implemented and which are left on the shelf: the payback period. It is quickly calculated, everyone understands it, and it feels like commercial prudence. That is exactly why it is so widespread. And exactly why it costs so much money.

Because the payback period answers a different question from the one that actually needs to be asked. Anyone who bases investment decisions on efficiency and decarbonisation measures around it systematically screens out the wrong projects. This article shows why that is the case, which metrics should actually carry the decision, and why in the end no single number is enough – what is needed is a decision basis that reflects several dimensions at once.

What the payback period says, and what it does not

The payback period relates the investment amount to the annual savings. That is the calculation. It is not wrong. It is only incomplete in a way that is routinely overlooked in practice.

This is not a marginal observation. It is the documented core of the problem. State authorities, the German Energy Agency and the relevant VDI guidelines on economic assessment (VDI 6025, VDI 2067) have been pointing it out for years: for investments with a long service life – and most energy and efficiency measures fall into that category – looking at the payback period alone leaves substantial economic potential untapped. Projects fail against required, often arbitrarily short payback limits, even though they would be highly profitable over their lifetime.

The blind spot: service life

The decisive fallacy lies in assessing a lasting effect with a one-off metric.

Take two measures at one site:

By the payback criterion, A wins clearly – half the time to return. A company with an internal limit of "three years maximum" would reject B and implement A.

Calculated over the service life, the picture reverses completely:

The measure screened out by the payback criterion is the one worth eight times as much. Exactly this mechanism runs unnoticed in many companies, year after year. Not because anyone miscalculates, but because the right calculation is never made in the first place.

The metrics that should carry the decision

The financial answer to the problem is well known and standardised. Instead of static methods (payback, simple cost comparisons), dynamic methods consider the full service life and the time value of money. Three metrics are decisive here:

Net present value. Sums up all savings arising over the lifetime, discounted to today's value, minus the investment. If the net present value is positive, the measure creates value. It is the most honest single indicator because it captures the entire service life – precisely what the payback period leaves out.

Internal rate of return. The return the measure generates on the capital employed. This number makes efficiency measures comparable with other uses of capital: a replacement investment in production, an acquisition, the repayment of debt. For investors and management, that is the relevant language. Not "saves energy", but "returns X percent".

Annuity. Distributes investment and savings evenly across the service life and shows the annual surplus. Useful when measures with different lifetimes have to be compared directly.

Why the right metric still is not enough

At this point one could end the article: payback out, net present value in, problem solved. In practice it is not that simple. And the reason matters more than the question of metrics itself.

First: Research on the so-called implementation gap – the well-documented phenomenon that efficiency measures are not implemented despite proven profitability – shows that the real barrier is rarely the calculation method. It is the transaction costs of the decision: lack of market overview, search and information effort, the sheer work of knowing which measures are viable at which site and in which order they pay off. A better metric does not help if nobody has the time to calculate it properly for thirty possible measures across twelve sites.

Second: A real investment decision is never made on a single metric. The plant manager deciding on a measure weighs several things at once: the return, yes, but also technical feasibility under the specific conditions of the installation, implementability during ongoing operations, and acceptance among the technicians who ultimately have to install and maintain it. Anyone who ignores these factors and puts only one number on the table produces a decision paper that convinces in the management meeting and fails on the shop floor.

And third, the point that almost always gets lost in a purely financial view: the same measure pays into several objectives at once. The sealed compressed-air line, the variable-speed compressor, heat recovery – each of these measures reduces operating costs and energy consumption and CO₂ emissions in one go. This is not a trade-off between profitability and climate action where one has to be weighed against the other. It is the same lever. The tonne of CO₂ saved is the by-product of the kilowatt-hour saved. You do not have to pay for it separately; you get it along the way. An assessment that shows only the euro or only the tonne conceals half the value of the measure.

What a robust decision basis has to deliver

From all of this follows what an efficiency decision really needs, beyond the one convenient number:

Conclusion

The payback period is not wrong. It is simply the answer to a smaller question than the one on the table. Anyone deciding on efficiency and decarbonisation measures is deciding on lasting effects, on several objectives at once, and on a multitude of competing options across different sites. A single, static metric cannot capture that. It screens out the wrong projects and leaves exactly those measures on the shelf that create the greatest value over their lifetime.

The financial tools to do better exist and are standardised. What is missing in practice is rarely the method. It is the capacity to apply it consistently to all measures across all sites and to turn the result into an order that holds up in management as much as on the shop floor.

This is exactly where it is decided whether a quarter of economically addressable emissions actually turns into measures – or whether the calculation stays unopened in the drawer.

dauri creates decision papers for cost-efficiency and decarbonisation measures across multi-site operations.